PROJECT SUMMARY The overall goal of this project is to identify molecular regulators enabling immune suppressive properties of metastatic melanoma and define cell lineages that mediate therapeutic function of CD47 blocking antibodies. Our central hypothesis is that metastasizing melanoma cells avoid immune recognition by hyperactivating CD47 promoter through NRF1 transcription factor. Overexpression of CD47 then modulates tumor immune microenvironment in a way that inhibits melanoma destruction and antigen presentation by professional phagocytes while at the same time stimulating myeloid derived suppressive cells (MDSCs) that negatively affect T-Cell responses. When the proposed research studies are completed we will accomplish identification and characterization of potent molecular and cellular targets that regulate CD47 dependent escape of immune surveillance by metastasizing melanoma cells. Delineating these factors will also serve a clinically predictive value to allow patient selection based on their immune cell repertoire resulting in the prolonged curative responses and increased survival. Clinical significance of the proposed studies is also highlighted by the fact that we will be using immune- humanized PDX models to characterize our findings in the setting most physiologically relevant to the patient disease.